The launch of Facebook's application platform last year has tempted several mobile firms into taking their games onto the social network.

Digital Chocolate launched Tower Bloxx and Cafe Solitaire as Facebook games, I-play ported Bubble Town, and Distinctive Developments recently launched its new Anytime Pool game on Facebook first, with a planned mobile release later this year. And that's just three.

So how rich an opportunity is the social games market for mobile firms? One person who should know is Kristian Segerstrale, the former European MD at Glu Mobile, who left to set up his own social games company, Playfish.

It's released three Facebook games so far: Who Has the Biggest Brain?, Word Challenge and Bowling Buddies. They're currently all nestling in the Top 10 Facebook Games chart, racking up a combined 700,000 daily active users, and 300 million minutes of player engagement in May.

So, every mobile firm should pile in, right? Well, not quite. Segerstrale says the immediate opportunity is for mobile firms to promote their mobile games within existing social games on Facebook.

"As a channel for promoting awareness of your game with advertising, it's pretty good," he says. "You have a pre-qualified audience of people who enjoy gaming, and you can advertise your game with a 15-second video within a social game, and capture a large audience quite quickly."

Playfish is currently serving around two million video adverts per day within its Facebook games, for example. So far, many ads within these games are promoting other social games, though.

"There hasn't been many cases of mobile publishers talking to social games publishers about advertising, but we expect to see those coming up," says Segerstrale.

But what about mobile developers making their own Facebook games? Segerstrale warns of the danger of thinking social games are just like mobile games with a bit of connectivity added on top.

"Superficially, they're quite similar, and the games require similar production budgets to mobile," he says.

"But there are a lot of pretty big differences too. In terms of technology, you're using Flash, so instead of porting your game to 1,000 phones, you're worrying about different Flash versions and browsers. And distribution is completely different, requiring server-side competence, since you're serving all this stuff."

An even more fundamental difference between mobile games and social games is design-related, however. Segerstrale describes most mobile games as solitary experiences – games designed to keep players entertained when they have a spare moment. Not so for social games.

"It's exactly inside out," he says. "Instead of designing for solitary engagement, you're trying to get the player involved in the game in such a way that the game becomes an object around which that person interacts with their friends. It almost becomes what's outside the game, rather than the core gameplay itself."

Other design differences are equally important. Segerstrale says releasing social games is much closer to the Web 2.0 mindset, with beta versions that you then improve over time, based on user feedback.

"It's about people interacting with you as much as it's about creating something for them to play," he says. "We've gone out of our way to work with people who understand this Web 2.0 way of doing things."

So far, many mobile firms' interest in social games has focused on creating something that promotes the mobile version – Tower Bloxx is an example of this strategy.

How about making completely new social games as a revenue stream in their own right, though? Which leads to the pressing question of how you can make money from a Facebook game, if you can at all.

"It's clear that the main sources of monetisation for social games will be a combination of transactions and advertising," says Segerstrale. "We've been encouraged by the ad inventory that we've attracted. As of today, we serve more than three million gameplays a day, which allows us to have a rich media inventory of over 60 million impressions per month."

But he says Playfish is keen to develop more transactional revenue going forward, which could be through charging for enhanced features within games, or through social expression. "In the context of play, if you have the coolest avatar or coolest kit, that might also be a source of revenue," he says.

In many ways, the model is already being explored in other kinds of gaming, such as free-to-play MMOs that charge players to buy items, or virtual worlds where people can pay for clothes for their avatars.

The final question many mobile developers have about social games is whether they can use something like Facebook to build a brand, then bring it back to mobile and sell lots of downloads that way.

"I don't think that ports from mobile to Facebook will be particularly successful, but the same will apply to taking a Facebook game to mobile," says Segerstrale. "Social games are designed for playing together, and that's not really happening on mobile today, so direct ports won't be successful."

However, he's more enthusiastic about the increasing convergence between PC and mobile, with mobile users using fully featured web browsers to access the same content as people on PCs.

"There is a period of time within the next three to five years when it's relatively likely that people will see one internet as opposed to one on a PC and one on mobile," he says. "There may be a convergence in games then, where people will be playing similar types of casual games on their browser on a mobile phone."